A bag contains 12 white and some black balls. If the probability of drawing a black ball from the bag is thrice that of drawing a white ball, find the number of black balls in the bag.
Given, Number of white balls = 12 Let x be the number of black balls. Total number of balls in the bag = 12 + x Also, the probability of drawing a black ball from the bag is thrice that of drawing a white ball. ⇒ x/(12 + x) = 3[12/(12 + x)] ⇒ x = 36 Hence, the number of black balls in the bag = 36
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